The present invention relates to photosensitive material for electrophotography having a surface coating layer on a function-separation type multi-layered photosensitive structure for use in printers, digital copiers, and the like.
Conventional photosensitive materials for electrophotography include selenium type, OPC type, and so forth, and among them, the selenium type is excellent with respect to resolution power, durability, electric properties and circumstantial resistance. However, the drawbacks of using selenium lie in that it has sensitivity only up to about 550 nm, except for crystalline selenium which is panchromatic. Further the surface of selenium photosensitive material crystallizes even at a slight temperature elevation which makes the material unusable. In light of the above, various elements have been added to the photosensitive material to overcome such drawbacks.
For example, tellurium has been used as an additive in photosensitive materials. Although the addition of tellurium can increase the spectral sensitivity as well contribute to the suppression of crystallization, if the photosensitive material is intended to be sensitive to semiconductor lasers (800 nm), the amount of tellurium required becomes excessive due to reduction in the residual potential and increase in fatigue. Consequently, a surface coating layer (OCL) is added for suppressing the electrical charges from the surface. However, most of the materials used in such a coating layer, such as pure Se, OPC and 4 wt % As - Se alloy, have extremely low hardness and are inferior in printing resistance.
In the case of adding arsenic to the coating layer in order to increase the spectral sensitivity, heat resistance and sensitivity are improved as the amount of arsenic is increased. However, since the effective sensitivity region is only up to 700 nm, a coating layer containing arsenic is not suitable for semiconductor laser light sources with wave lengths at 800 nm.
The object of the present invention is to provide a photosensitive material for electrophotography capable of overcoming the foregoing problems, having sensitivity at long wavelengths and also excellent heat stability and printing resistance.